Recovery of tin from scrap tin plate and like tin bearing materials



May 24, 1932. M. G. GILB'ERT- 1,859,919

RECOVERY OF TIN FROM SCRAP TIN PLATE AND LIKE TIN BEARING MATERIALS Fi1 ed Oct. 25, 1929 Patented May 24, 1932 ease ATE

MASON enonen GILBERT, orronr ELIZABETH, soorn arnroaessrcnon To THE ,AFRZCAN TIN RECOVERY COMPANY LIBIITED; OF FOR-'1" ELIZABETH, SOUTH AFRICA,

A COMPANY 0F THE UNION OFSOU'IH AFRICA.

nncovnnv on TIN rnoiascnar TIN'PLATEAND s geammals ailments Application fi ea October 23, was, Serial No.

applicable also to the extraction of tin from rying metals tin-containing alloys such for example as solder and White metal.

Processes have been proposed for the recovery of tin from scrap metal in which there is employed a solution consisting of a lead compound such as litharge. dissolved in a solution of caustic soda or potash.

According to the present invention a process for the recovery of tin from tin-carof the kind described by treatment with an alkaline solution (preferably caustic) of a'soluble leadsalt is characterized by the fact that the soluble lead salt is lead acetate. A preferred alkali for the preparation of the solution is caustic soda.

It is found that a' solution of this description gives a peculiarly rapid and complete action which may be described as instantaneous.

vantages in the process. F or example, the

point at Which the solution is exhausted of one and the bath up to this point with suclead is a noticeably sharp can be used right cess.

Preferably the treatment is effected with a hot solution (for example a solution maintained at or near its boiling point).

The efiect of the immersion of tin-carryti on of finely divided lead upon the iron plate The lead, however, 7

or other residue metal.

is not adherent to the residue metal and can readily be recovered. The tin passes into solution in the extracting bath and can be readily recovered from the resultant liquor.

According to a further feature of the in- It also leads to certain operating ad-.

401,904, are Great :Britaiii January 15,1929,

vent-ion, the resultant tin-containing 1 solution' is treated with areagent, for example carbon dioxide, which vvillprecipitate' the tin from the solution. The tinisprecipitatd in the form of metastannic acid. in every pure condition. The solution from Which tin has thus been precipitated may be treat-ed for example with burnt lime to regenerate ca usticalkali for re use in the process. An alternative method of recovering the tin" 1n the tin-contamingsolution is to treat the solution With milk of lime. This precipitates thetin inthe form of calcium stannate and't'he residual solution ofcaustl'c soda is returned to the'process. i

i The solution after treatment With limev for the precipitation of the dissolvedtin as cal c um stannate containscalcium acetateand caustic alkali Since caustic alkali is less solubleina hot solution maybe cium acetate. i a p v y 1 Again, thetin may, if desired, be precipitated in metallic form bythe addition of a suitable subdivided I metal, for example heated to precipitate the calgranulated zinc.'

It is an important advantage of the use of an extracting .solution according to this invention that the solution givesup the Whole of its lead and in consequence the tiniprecipitatedfromthesolution is entirely free from contamination With lead. In addition. continuous regeneration of the active-lead salt solution, for example as hereinafter desc'ri'bed,is greatly facilitated.

The lead precipitated from the solution duringthe dissolution of the tin may be treats. ed Withacetic acid whereby lead acetate is regenerated, for employment again in the process. 7 In the process of this invention, in con; trast to the'case Where lead oxidesu'ch ,a-s massicot or litharge is dissolved in; caustic alkali solution, all the leadof the lead salt instead, .ofonly about one half of it, is available in, an active condition. An alkali plumbite is formed Without at the same time the formationlof aplumbate, These facts result in a very complete reaction. 4

One form of the process will now be desolution than ina cold, th

scribed by way of example with reference to the accompanying drawing which illustrates' diagrammatically an apparatus in which the process may be carried into effect:-

The apparatus comprises a de-tinning vat 11 in which rotates, partially immersed, a perforated drum 12 to receive scrap metal. The drum has a feed-chute 13 at one end, flights 14 to direct the material forwardly and lifters 15 at the discharge end. The lifters 15 discharge the de-tinned scrap into a discharge chute 16 whence it passesinto a washing tank 17 under a water spray 18. The de-tinning liquid in the tankll is heated by a steam coil 19. r

Exhausted liquid from the tank; 11 is de livered by a valve 120 to a de-tinning tank 21 whereit is subjected to the action of carbon-di-oxide supplied through a valve 22. Fromthe vat 21 the liquid, deprived of its tin, passes through a. valve 23 to a causticizing vat 24 containing an agitator .25 for stirring the liquid with, burnt lime; Re-

' generated caustic alkali is re-delivered to the tank 11 by the pump 26 through a valve 27 Lead sludge which collects in the bottoms of the vats 11 and 17 is periodically removed and shovelled into an acetic .acid'tank 28 where lead acetate is formed. Thelead acetate is pumped by a pump 29 to the de-tinning vat- 11 through a valve 30.

In carrying the process into effect the vat 11 is filled with a mixture of 20% lead acetate solution into which has been added a 20% sodium hydroxide solution until the white- .cloud formed on addition only just disappears. The solution so formed which is of alkaline reaction, is heated by the steam coil 19 nearly to boiling point. WVaste tin plate is delivered by the chute 13 into the drum 12 where it is immersed in the solution and by rotation of the drum tumbled about. This not only ensures thorough contact with the solution, but also causes the lead which is precipitated to be washed off andto fall as a sludge to the bottom of the vat. The detinned scrap delivered into the Washing tank 17 is washed by the water sprays free of any remaining precipitated lead, and is then taken away and disposed of. The other operations follow as above described.

In the treatment of alloys it is desirable that the alloy material, such as scrap white metal, should be broken up or disintegrated as small as possible.

I claim:

1. A regenerative process for the recovery of tin from tin-carrying metals which consists in treating the tin-carrying metal with a hot caustic alkali solution of lead acetate so as to dissolve tin from the tin carrying metal and precipitate spongy lead, treating the resulting spent de-tinning solution to precipitate tin therefrom and recover caustic 3. The process according to claim 1, where-' in the spent de-tinning solution is treated with carbon dioxide to the solution and thereafter with burnt lime to regenerate caustic alkali.

precipitate tin from L 4. A process according to claim 1, 'wherep in the spent de-tinning solution istreated with milk of lime to precipitate tin from the solution as calcium stannate.

In testimony whereof I affix my signature.

- MASON GEORGE GILBERT. 

